Comment by Bostonian
3 months ago
In modern Fortran, functions should be pure (although the language does not require this), and procedures that mutate arguments are made subroutines (which do not have return values).
3 months ago
In modern Fortran, functions should be pure (although the language does not require this), and procedures that mutate arguments are made subroutines (which do not have return values).
Note that Fortran's interpretation of the term "pure" bizarrely allows a "pure" subprogram to depend on mutable state elsewhere (in a host, a module, or a COMMON block). So Fortran's "pure" functions aren't referentially transparent.
(F'2023 added a stronger form of "pure" and calls it "simple", but it didn't strengthen the places where a "pure" procedure should be required to be "simple", such as DO CONCURRENT, so being "simple" will be its own reward, if any compiler actually implements it. And a "simple" function's result value can still depend on a mutable pointer target.)